A vehicle's resistance to movement due to its rear section is known as base drag.
The fluid flows that have difficulty following the rear profiles of moving vehicles become turbulent behind the vehicle, which reduces pressure at the rear of the vehicle and creates a strong resistance to the vehicle's forward movement.
Passive solutions exist that reduce the rear drag of vehicles and in particular solutions are known wherein a vehicle's rear profile is realized as a cone by using an inflatable bladder as described for example in document DE 41 01 960, adding flow deflection profiles as described for example in document EP 0 273 850, one or more annular appendages as in document U.S. Pat. No. 6,297,486, lateral deflectors as in document U.S. Pat. No. 6,926,345.
Other realizations are based on active means such as mobile slats as described in document U.S. Pat. No. 4,411,399 or an injection of fluid in the rear of the vehicle in order to fill the depression.
Aerial vehicles propelled by jet engines present a jet pipe propelling nozzle and the jet engines only create a small amount of drag because the jet of ejected gases plays a role in the vehicle's aerodynamic profile.
In contrast an unused engine creates an enormous amount of drag (up to one third of the vehicle's total drag).
That is why, for example, when the American space shuttle currently in service is transported by airplane, it is equipped with a conical rear cover masking the nozzles of its rocket engines.
On the other hand, this cover cannot be used when this shuttle is launched because it would be necessary to jettison it before igniting the rocket engine, which would entail designing a cumbersome release device ensuring that no debris could damage the shuttle or the boosters.
Similarly, removable active devices are difficult for a space plane to use because they are heavy and require devices for operating them.
Furthermore, these systems are complex to implement, since they must be deployed without creating additional drag themselves when the rocket engine is ignited, which occurs in atmospheric flight.
Similarly, using active fluid-injection devices would require the fluid to be carried in the vehicle, which would reduce its payload.